Recently image capturing, displaying and in particular encoding has improved from so-called low dynamic range (LDR) imaging (such as classical systems like PAL or MPEG2) to so-called high dynamic range imaging (HDR). Illuminances in nature can range from 100,000 lux in sunlight, over typical office or room illuminations of around 500 lux, to e.g. 0.051× under quarter moonlight. Luminances (L) in the world range from 1 billion nit of the sun disk, to 10,000s of nits for lamps, to a couple of (ten)thousands of nit for objects in sunlight (like a building, cloud rims, or a white paper), to hundredths or 10s of nits for objects under (heavily) overcast sky or indoors, to 0.1 nit for a white paper under moonlight, etc. This doesn't necessarily mean one should render these luminances on a display in exactly the same way, rather, the picture should look artistically good, meaning at least that there should be approximately similar appearance differences for the regional luminances of objects when rendered on the display screen. One should understand that tone mapping for rendering on a particular display is with the many displays existing nowadays decoupled from either capturing or coding, leading to three linked representations. In general, a requirement of HDR imaging to be able to render e.g. a bright white wall differently from an adjacent bright lamp on a display, is that their respective pixels are also encoded with different luma (Y) values. Sensors or cameras are becoming more powerful in that indeed they can capture most of those many different luminances in the world faithfully (whether with larger well-depths, differently exposed pictures, etc.), and for simplicity we shall consider their native color representation to be a linear luminance encoding within [Lmin, Lmax]+chromatic information. We may then use an entirely arbitrarily specified definition (according to desired requirements of course, such as e.g. later processability of the encoded information like local brightening, or data compression concerns, etc.) for our transmission codec. Lastly this encoded data (Y_C1C2, or similar) can then again be converted in many ways to a rendering-side representation, which we can for simplicity equate with driving values for e.g. the LCD pixel colors. Displays are getting more renderable dynamic range, so that they can firstly render more bright regions, and secondly simultaneously or successively more dark regions. This allows placing all these various luminance objects along the renderable gamut with optimal rendered output colors.
A considerable problem for content creators is that, despite their efforts to protect their content so that it can be duly sold instead of illegitimately copied, all kinds of pirates do distribute the content and sometimes in large numbers. When designing a new image encoding standard, apart from looking at how to represent pixel colors from e.g. a data compression point of view, one can have as an object simultaneously engineer in new requirements, such as protectability of the standard. We came up with a way to encode HDR images in such a way that they are actually represented as LDR images, plus a set of transformation strategies to recuperate from all the HDR effect information encompassed therein the original HDR image again. We can then relax the constraint of content protection somewhat. The image (texture/pixel) data itself may be hacked, but then the pirate has a lousy picture, not the original HDR master grading. The transformation strategy—which in our framework is at the same time a co-encoding of the master HDR graded image, and a legacy usable LDR variant—can then be protected strongly, e.g., this other half of the HDR information in our new codec can be transmitted securely only during viewing (and e.g. never go outside the hardware of an image processing IC if it also moves over data connections decrypted, and is deleted from within—IC temporal memory as soon as possible). This would allow applications with better control when the content creator wants to sell HDR movies, e.g. he may sell in fact only the HDR recuperation functions or algorithms.